In tube or bag filters for the removal of particulates from a gas, it is known to provide a filter housing in which the tubes of gas-permeable material are disposed in rows and are vertically oriented. It is also known, e.g. from German patent document--Printed Application--Auslegeschrift DE-AS No. 1,298,399, to provide the tube carriers as rods or bars which are mounted in holders or yokes which carry swingable actuating levers radially engaging around the tube carriers and having free ends connected to a bar which is shiftable for common actuation by an excentric or crank drive. The reciprocating movement of the bar can raise and lower the upper end of the tubes. The result is an expansion and contraction of the tube which derives from the pivotal movement of the holder and causes accumulated dust deposits on the filter material to be released. The dislodged dust falls through the filter space and can be collected in a bin or the like at the bottom of the housing from which the dust is removed by a worm. The worm can carry the dust through a discharge gate preventing the release of gas into the atmosphere.
With the conventional devices of the aforedescribed type, the expansion and contraction movements of the tubes of filter material are a result of the pivotal movement of outrigger-type arms caused by the excentric drive. To ensure a rapid expansion and contraction cycling, a correspondingly rapid movement of the excentric drive is required, i.e. the excentric shaft must be rotated at high speeds. This of course means that the shiftable bar and the connecting rod tied to the latter must also be operated at high speeds.
Experience has shown that the need to operate the bar, its drive and the connecting linkage at such high speeds requires massive construction with low tolerances to minimize wear and hence raises the cost of the filter. Furthermore, because of the friction and the masses which must be accelerated and decelerated for each cycle, the energy consumption is high and hence the filter is energy inefficient and expensive to operate.
It should be understood that, as one requires higher speeds for the mechanisms described, the forces which must be absorbed by the moving members and the guides or supports therefore are correspondingly increased.
As a consequence, the art has tended to resort to less positive methods of dislodging dust from filter surfaces, namely, the so-called rapping techniques, whereby the holders for the filter surface are periodically or intermittently impacted by a rapper.
In such systems, the holders for the filter tubes can extend through the roof of the filter housing and there provided with tilting-like formations cooperating with cam disks with sudden drops whereby the filter tubes are gradually expanded and, at the sudden drop, are spontaneously released. The lever can then be allowed to drop against the stop to provide the rapping action.
Rapping systems of this type, however, have similar disadvantages with respect to the high cost of the filter and, while rapid dislodging motions can be provided, the loading of the filter material is nevertheless high so that considerable stress is applied.
Perhaps more importantly is the environmental hazard created with filters of the latter type because of the amount of noise made by the rappers.